Certain circuit boards, particularly of the type often used in power supply units, become routinely interconnected with typical insulated electrical conductors. At an end of such a conductor a portion of the insulation is typically stripped back and a closed or open terminal lug is attached to the conductor. Such terminal lug may then be fastened by a typically hardened clamping screw to a terminal seat on the circuit board.
In the past, terminal seats in circuit boards were often machined parts having blind, threaded passages leading from seat-type pedestals into stud-like extensions. The extensions were inserted into plated thru holes of circuit boards and soldered into place. The terminal lugs then became fastened to the pedestals by typical, hardened terminal screws.
A problem with machined screw terminal seats relates to typical dimensional tolerance ranges of mass produced screw threads. The insertion torque of the terminal screws tends to vary widely. In some instances the screws thread easily into the seat with little resistance. Thus, unless the screw heads are seated very firmly against the respective lugs, the screws, and hence the terminal lugs, exhibit a tendency to loosen and to become electrically disconnected, thereby rendering any associated apparatus defective.
Non-threaded terminal seats having extensions of triangular cross sections are commercially available. Such seats may be positioned and soldered into triangular apertures in a circuit board, and screws may be threaded into the initially non-threaded extensions. Threads form in portions of each of the three interior walls of the extensions, and the three corners of the extensions of the seats act as reliefs in thread-forming operations. Problems appear in orienting the extensions of such seats with respect to corresponding apertures through the circuit boards wherein the terminal seats are to become located.
Also, as a hardened screw is rotatably inserted into the cylindrical extension of the terminal seat to form the threads therein, wall portions engaged by the threads are urged outward and cause stresses in the circuit board. Such stresses are undesirable in that they tend to result in cracks in metallized areas. Such cracks, if they are allowed to progress, may ultimately bring about a failure in their host circuit board.